Equipment stress monitor

ABSTRACT

An electronic apparatus that includes means for determining the temperature stress the equipment has been subjected to is disclosed that includes a multiplexer with a plurality of inputs that read the temperature at various locations on the equipment being monitored. The temperature at each location is measured regularly to determine in which of a number of different-sized temperature bands it lies, thereby providing an indication of the stress to which the equipment is subjected.

BACKGROUND OF THE INVENTION

The present invention relates to electrical or electronic apparatus.

It is well-known that the expected life-time of electronic apparatus isvery dependent on the temperature to which the apparatus has beensubjected. For example, the expected life-time of semi-conductor basedproducts may be halved for each prolonged rise in temperature ofapproximately 10 to 20° C. It is possible to formulate theoreticalexpectancy equations which relate the expected remaining life-timeagainst time already operated at a certain temperature, from whichestimates for the expected failure for the product can be established.However such equations are only valid on a large population, so for auser of only a few pieces of equipment it is not feasible to use thisapproach.

The present invention provides electrical or electronic apparatuscharacterised by means to determine in which of a plurality ofpredetermined temperature bands of differing size temperature ranges theapparatus ambient temperature is and means to record outputs of thedetermination means.

In this way, there is produced a record of the degree of stress to whichthe apparatus has been subjected and so allows the user to have anindication of how the life-time of the product has been shortened. Byhaving temperature bands of differing sizes, careful and accuratemonitoring of temperature regions of particular interest can readily beachieved. In one example, size of a band decreases with increasedtemperature.

BRIEF SUMMARY OF THE INVENTION

The invention may have any one or more of the following features:

(i) the determining means is operable on a number of temperature bandswith temperature ranges of different sizes such that the size of thetemperature range in a band decreases for increased values oftemperature;

(ii) the frequency of measurement by the determining means is dependenton the temperature band;

(iii) the frequency of measurement increases as the temperature band ofthe previous measurement(s) increases;

(iv) the apparatus ambient temperature comprises a temperature valuebased on the temperature of a section of the apparatus and/or theenvirons of such a section;

(v) multiplexing means to switch the determining means between aplurality of measurement locations on the electronic apparatus and/orbetween a plurality of measurement locations on different pieces ofequipment;

(vi) means to estimate failure or deterioration based on output from thedetermination means and/or the recording means.

The present invention also provides a method of monitoring electronicapparatus comprising determining in which of a plurality ofpredetermined temperature bands of differing size temperature ranges theapparatus ambient temperature is and recording outputs of thedetermination means.

The information resultant from the invention can be used in a variety ofdifferent ways. For example, the information can be displayed to theuser of the apparatus by an appropriate display means e.g. a hand-heldterminal, a PC screen (whether LCD or cathode, ray tube) or a printer.Alternatively or additionally, the information can be stored for uselater e.g. when the apparatus is being maintained, serviced and/orrepaired; such information would also be of assistance to themanufacturer in quality analysis and/or predicting failure-rates orlife-times of subsequent apparatus.

The invention is applicable to a wide variety of types of apparatus,including in particular controllers, recorders, programmers, also flow,pressure or temperature transmitters.

The invention is particularly beneficial because the results achieved bythe apparatus and method of the invention can be applied to certain wellknown and well-defined relationships of aging and stress againsttemperature, thereby resulting in accurate life-expectancy predictionswhich can readily and simply obtained. Such characteristics forelectronic and electrical equipment follow well-defined processes andequations, so that monitoring according to the present invention cangive very valuable information on expected failure, whereas mechanicalequipment do not follow such well-defined processes because otherless-precise operations are involved including e.g. motion of parts,mechanical stress, metal fatigue.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In order that the invention may more readily be understood, adescription is now given, by way of example only, reference being madeto the accompanying drawings, in which:

FIG. 1 is a block schematic drawing of a circuit embodying the presentinvention;

FIG. 2 is a graphic representation of information derived from thecircuit of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a stress monitor generally designated as 1 within atemperature transmitter, the monitor 1 having a multiplexer 2 with anumber of inputs 3 to 6 for temperature sensing at a number of locationswhile (for clarity), FIG. 1 does not show the inputs for process signalse.g. of pressure, flow, temperature. Thus inputs 3 to 6 are for signalsrepresenting the ambient temperature at various locations indicated by(i) 3¹ on the housing of a thermowell associated with the temperaturetransmitter, (ii) 4¹ on the printed circuit board of the thermowell,(iii) 5¹ on the housing of the main unit of the transmitter and (iv) 6¹on the printed circuit board of the main unit. The ambient temperatureis measured using the cold junction temperature sensor of athermocouple.

A microcontroller 7 passes selection signals 8 to multiplexer 2 tocontrol switching of multiplexer 2 between inputs 3 to 6 and a zerooutput mode, such that multiplexer 2 outputs appropriate signalsrepresenting temperature for each of locations 3¹ to 6¹ at a frequencysuitable for the respective locations and for the respective temperaturevalues as explained below. Each temperature signal output frommultiplexer 2 passes to amplifier 9 for modification to the appropriatelevel required for A/D convertor 10 which provides the signal for inputto micro controller 7.

Typically, the temperature at each location is measured once in aspecified time, e.g. every 5 seconds. Each measurement is compared tothe previous one and, if it does not exceed the previous one, it isdumped; if it exceeds the previous one it is stored in RAM 11 and theprevious one is dumped. After an hour the stored value, which is thehighest temperature measured in that hour, is used in determining whichtemperature band is to be allocated to that hour period. The process isthen repeated for the next hour period. However, in a variation, thefrequency of selecting a temperature signal from each location (i.e.corresponding to the 5-second sampling above) and/or the frequency ofdetermining and recording the relevant temperature band is or aredependent on what the location is and also the last temperaturerecording and/or sampling for that location. Thus the frequency ofeither or both operation increases when the temperature of that locationincreases and thereby the potential for stress effects increases. Ifthere is some potential or actual relationship between temperaturechanges (whether in the same or opposite directions) in two or morelocations due eg. to proximity or similarity in positions or components,then there may be appropriate changes in selection frequency of one suchlocation commensurate with a change in selection frequency of anothersuch location.

At microcontroller 7, the signal is processed so as to determine inwhich of a number of temperature bands it lies; each location has itsown set of temperature bands and, for each set of temperature bands, thebands become smaller in terms of the size of the range of temperaturesas the temperature increases. In this way, due account is taken of theaccumulation or increase of stress which arises due to temperature withappropriate increased accuracy and definition with heightened stress.

FIG. 2 represents graphically the temperature bands I to VIII forlocation 3¹, namely the housing of the thermowell. The first temperatureband I covers 0° C. to 30° C. i.e. a range of 30° C., whereas the nexttemperature band II has a reduced range of 20° C. and the subsequentband III has a further reduced range of 15° C., and so on.

Once microcontroller 7 has determined in which temperature band thesignal lies, the information is passed to RAM store 11 enabling varioustreatments e.g. averaging and filtering, and then non-volatile memory 12is up-dated. Microprocessor 7 also sends the information to a display 13which provides a representation of the accumulated time recorded foreach temperature band, as shown on the right-hand side of FIG. 2. Thisdisplay gives the user an indication of the degree of excessivetemperature to which the thermowell housing 3¹ has been subjected andenabling the user to estimate readily and easily the shortenedlife-time. Such analysis can be accurate and hence very valuable to theoperator because the stress/temperature relationship for electrical andelectronic equipment is well-known and well-defined, much more so thanfor mechancial equipment which is subjected to many more variables, atleast some of which are not well-defined or readily predictable.

The information on the temperature bands may also be input (eitherdirectly from microcontroller 7 or via RAM 11 or memory 12) into otherequipment e.g. a hand-held terminal, a PC display (whether LCD orcathode ray tube) or a printer.

The data can be presented in any appropriate form e.g. on a PC screen itcan be done in a histogram form, with the temperature band on the x-axisand the hours on the y-axis.

As well as being used by the user of the equipment, the accumulatedinformation in memory 12 can be used when the product is beingmaintained, serviced or repaired; also the information can be used forquality analysis by the manufacturer.

The information collated under the invention can be used to predictand/or estimate failure and/or deterioration.

In an alternative version, the stress monitor can be embodied as a pieceof equipment (whether stand-alone or incorporated into a controller orother apparatus) which monitors a number of separate products whether ofthe same type or different types e.g. flow transmitters, temperaturetransmitters, pressure transmitters, printers, valves, flow-meters.

The present invention has been described with particular reference tothe preferred embodiments thereof. It will be obvious that variouschanges and modifications can be made therein without departing from thespirit and scope of the invention as defined in the appended claims.

What is claimed is:
 1. An electrical or electronic apparatuscomprising:means to determine in which of a plurality of predeterminedtemperature bands of differing size temperature ranges the apparatusambient temperature is, based on a measurement of the value of thetemperature of at least one section of the apparatus, the frequency ofmeasurement being dependant on the temperature band and the frequency ofthe measurement increasing as the temperature band of the previousmeasurements increases, whereby the sizes of the temperature ranges inthe bands decrease for increased values of temperature; and means torecord outputs of the determination means.
 2. The apparatus according toclaim 1 wherein the measurement of the value of temperature is based onthe measurement of the temperature of a plurality of sections of theapparatus, said apparatus including multiplex means to switch thedetermining means between the plurality of measurement sections on theapparatus.
 3. The apparatus according to claim 1 wherein the recordingmeans comprises RAM means.
 4. The apparatus according to claim 1 whereinthe recording means comprises non-volatile memory means.
 5. Theapparatus according to claim 1 wherein there is further included toestimate failure or deterioration of the apparatus based on output fromthe determination means and/or the recording means.
 6. A method ofmonitoring electronic apparatus comprising the steps of:determining inwhich, of a plurality of predetermined temperature bands of differingsize temperature ranges the apparatus ambient temperature is, based on ameasurement of the value of the temperature of at least one section ofthe electronic apparatus, the frequency of measurement being dependanton the temperature band and the frequency of the measurement increasingas the temperature band of the previous measurements increases, wherebythe sizes of the temperature ranges in the bands decrease for increasedvalues of temperature; and recording outputs of the determination means.7. The method according to claim 6 wherein the measurement of the valueof temperature is based on the measurement of the temperature of aplurality of sections of the electronic apparatus, and the determiningstep comprises multiplexing between the plurality of measurementsections on the electronic apparatus.
 8. The method according to claims6 wherein the recording step comprises inputing into RAM means.
 9. Themethod according to claims 6 wherein the recording step comprisesinputting into non-volatile memory means.
 10. The method according toclaim 6 wherein there is further provided the step of estimating failureor deterioration of the apparatus based on the determining or recordingstages.
 11. The apparatus according to claim 2 wherein there is providedat least a second apparatus having at least one section of said secondapparatus connected to said means for determining the measurement of thevalue of the temperature of the second apparatus section and saidmultiplex means switches the determining means between the apparatusmeasurement section and the second apparatus measurement section. 12.The method according to claim 7 wherein there is provided at least asecond electronic apparatus having at least one section of said secondelectronic apparatus arranged for the measurement of the value of thetemperature of the second electronic apparatus section, and said step ofdetermining comprises multiplexing between the electronic apparatusmeasurement section and the second electronic apparatus measurementsection.